The present invention relates to a golf ball having an excellent durability to repeated impact and a good flight performance.
Most golf balls currently in use are manufactured by employing a process such as injection molding or compression molding to coat a material composed chiefly of urethane resin or ionomer resin around a solid core that is generally made primarily of a rubber such as a diene rubber.
The main features required of a golf ball include distance, controllability, durability and feel; balls having these qualities in the highest degree are always desired. At the same time, a succession of golf balls with three-piece and other multilayer constructions has emerged in recent years. By providing golf balls with a multilayer construction, it has become possible to combine many materials of differing properties, and apportioning ball features among the respective layers has created possibilities for diverse ball designs.
Generally, in cases where the distance traveled by a golf ball is regarded as important, the core or cover is formed so as to be rather hard, thereby increasing the resilience of the ball when struck. In such a case, the distance can be extended, but the ball tends to have a hard feel, making the sense of exhilaration that is sought when playing the ball difficult to achieve. To address this concern and improve the feel, it is necessary to form the ball so as to be somewhat soft. However, because the ball will then have a lower rebound and a greater spin receptivity on shots with a driver, an increase in the distance will be difficult to achieve. Also, in such soft (low-hardness) balls, it is common to use a cover that employs a rather soft, crack-resistant, ionomer resin, but this tends to result in a poor scuffing resistance. The above rebound and scuff resistance may be improved by using a hard material in the cover, although when the cover is formed to a degree of hardness at which the desired rebound and scuff resistance are attainable, the cover becomes incapable of following deformation of the ball on impact, giving rise to the early onset of cracking.
While it is possible to improve the rebound and reduce the spin rate by forming an intermediate layer of a highly neutralized ionomer resin composition in which the ionomer resin degree of neutralization has been increased through the addition of a basic inorganic metal compound, the resulting ball often has a poor durability.
Hence, there exists a desire to satisfy at the same time the conflicting demands of improved distance, durability and feel. In particular, there is a desire for the development of a soft golf ball having an excellent feel which achieves both a good flight performance and has an excellent durability to repeated impact.
Prior art related to the present invention includes the three-piece solid golf ball disclosed in JP-A 2001-79116, which has an outermost layer composed of various types of thermoplastic elastomers to which a granular inorganic filler has been added. In addition, JP-A 2003-761 discloses a golf ball in which an inorganic filler has been included within a cover material composed primarily of an ionomer resin, and JP-A 2003-126298 discloses a golf ball wherein an inorganic filler has been included in a high-hardness resin.